First of all, this depends on the country. In some places, PhD students are considered workers, and have the social rights that come with it. I still work a few more hours than what my contract says, because it goes in my own benefit, but it would be illegal for my advisor to force me to work overtime (so, answering your question, no, here it is not normal).
In other places, they don't, so they may be in principle allowed to demand as much as they want. But here we have a problem: double the hours doen't mean double output. In general, it is not true that working more hours you will get more results!
The best argument to show this is that big tech companies, like Google and Yahoo, that are probably the closest thing to Academia in the industrial world, go to lengths to limit the overtime their engineers put in. Their beans are in the quality of the output, so they have done extensive and careful research, and it has one of the highest quality assurances: lots-of-money-reviewed.
Sometimes, there are deadlines, and we have to put in extra hours; but then, you will get much better results if your team is not burned out.
Edit: Here is a study relating hours worked and productivity in a factory during the World War I. It appears that the productivity for this manual work scales linearly until it hits the roof at 50 h/week. It is remarkable that people working 72 h/week accomplished exactly the same as people working just two thirds of that.
Without more data to support it, I conjecture that for intellectual creative work, the plateau is reached much earlier.